Phonetic spelling of the military acronym HUA, which stands for "Heard Understood Acknowledged." Originally used by the British in the late 1800's in Afghanistan. More reciently adopted by the United States Army to indicate an affirmative or a pleased response.

Referring to, or meaning anything and everything except "no." Generally used when at a loss for words. Also:

Good copy, solid copy, roger, good or great; message received, understood.
Glad to meet you, welcome.
I do not know, but will check on it, I haven't the vaguest idea.
I am not listening.
That is enough of your drivel--sit down.
Stop sniveling.
You've got to be kidding.
Yes.
Thank you.
Go to the next slide.
You have taken the correct action.
I don't know what that means, but am too embarrassed to ask for clarification.
That is really neat, I want one too.
Amen.

1: heard understood acknowledged 2:i don't know what you said but i want you to think i was paying attention. 3:yes. 4: i disagree but i'll do it anyway. 5: i want you to think i care. 6: i want to show you i can act motivated. 7: hardcore, tough.